Loop Fermenter

Fermenters are usually classified based on their vessel type such as tank, column, or loop fermenters. The tank and column fermenters are both constructed as cylindrical vessels. They can be distinguished based on their height-to-diameter ratio (H/D) as (Schiigerl, 1982) ... 

A loop fermenter is a tank or column fermenter with a liquid circulation loop, which can be a central draft tube or an external loop. 

A loop fermenter is a tank or column fermenter with a liquid circulation loop, which can be a central draft tube or external loop. Depending on how the liquid circulation is induced, it can be classified into three different types air-lift, stirred loop, and jet loop (Figure 6.22). 

Fig. 6.22 Loop fermenters (a) air-lift, (b) air-lift with external pumping (c) ICI pressure cycle.

There have been many simple modifications to airlift bioreactors for specific applications. For example, a novel airlift loop fermenter (schematic unavailable in the literature) utilizes a side arm. The external loop in this integrated system overcomes the problem of ethanol inhibition by continuously stripping ethanol from the fermentation broth and recovering it by condensation. This is suitable for the simultaneous production and recovery of ethanol. ... 

While it is easy to add materials to a fermentation, removal is difficult. Membrane devices have been placed in the fermenter or in external recycle loops to dialyze away a soluble component. Cells release wastes or metabolites that can be inhibitory these are sometimes referred to as staling factors. Their removal bv dialysis has allowed cell concentrations to reach ten to one hundred times that of control cultures. 

Figure 2.5 Possible technological solutions to bioprocess problems a) Fed-batch culture b) Continuous product removal (eg dialysis, vacuum fermentation, solvent extraction, ion exchange etc) c) Two-phase system combined with extractive fermentation (liquid-impelled loop reactor) d) Continuous culture, internal multi-stage reactor e) Continuous culture, dual-stream multi-stage reactor f) Continuous culture with biomass feedback (cell recycling). (See text for further details).

In applications of airlift bioreactor there are various types of fermenter. The most common airlift bioreactors are pressure cycle, internal and external loop bioreactors. 

The cooling duty can be provided by either making the draught tube an internal heat exchanger or with a heat exchanger in an external circulation loop. The mass transfer coefficient for external loop airlift Fermenter is estimated as 8... 

Continuous extraction loop reactor Ethanol production with glucose fermentation Saccharomyces cerevisiae 126... 

Small scale equipment used for reactor process development in the biochemical field, such as small scale fermentation reactors and closed loop reactors, have their merits for general reactor development. These reactors may be as large as 20 liters in volume, and are well equipped and instrumented. They are not reviewed, however, in this book. 

There are a few other kinds of industrial plants. An air-lift tower fermenter was developed by ICI for the production of single-cell protein from methanol which employs an external loop for heat removal. Trickle beds for the treatment of waste waters employ packing structures or packing elements of 4-6 cm dia and porosities above 50%. Microbial films are formed on the packing that react with the organic substrate and the air as the liquid flows down and the air up. 

The second paper goes more into the hardware and programming needed for control loops in a production setting. Four fermentation models are used for this portion E. coli (unicellular), S. fradiae (filamentous), Pichia pastoris (unicellular), and CHO-K1 (animal cell line). Fermentation profiles are shown and strategies are discussed. 

FIGURE 4.5 Effects of solid-state enzyme treatment on (A) soluble fiber and (B) insoluble fiber contents in psyllium. P, the Pentopan Mono BG S, the Shearzyme 500 L from Novo Nordisk Ferment Ltd. (Switzerland) lOOP, 100 units of P 12S, 12 units of S and Psy stands for the commercial psyllium husks, the starting material for the solid-state enzymatic reaction (re-drawn from Yu and Perret, 2003a). 

If the final cell concentration is larger than CXopt, the best combination of two fermenters for a minimum total residence time is a CSTF operated at CXopt followed by a PFF, as explained already. However, the cultivation of microorganisms in the PFF is limited to several experimental cases, such as the tubular loop batch fermenter (Russell et al., 1974) and scraped tubular fermenter (Moo-Young et al., 1979). Furthermore, the growth kinetics in a PFF can be significantly different from that in a CSTF. 

Figure 6.8 Diagram of instrumental configuration of the LC/MS system used for characterization of crude fermentation extracts. The system consists of the following components (1) HPLC (2) loop injector (3) guard column (4) 5pm C18 HPLC column (4.6mm x 25cm) (5) zero dead volume tee (6) UV detector (7) fraction collector (8) triple quadrupole mass spectrometer equipped with ESI interface (9) ESI power supply and gas manifold and (10) syringe pump. (Reprinted with permission from Ackermann et al., 1996a. Copyright 1996 Elsevier.)...

This article presents the design and implementation of a software sensor for the continuous determination of substrate concentration based on a simple model of a fed-batch fermentation process and the available signals of two other sensors—one for on-line biomass determination (7) and the other for on-line ethanol determination (8)—developed in previous works. The software sensor proposed provides a continuous signal that can be used in a control loop to manipulate the substrate feed flow in order to maintain almost constant substrate concentration and obtain an excellent level of productivity and yield during all of the process, as shown in experimental control strategy studies in previous works (9). 

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